Thin film resistors (TFRs) are very attractive components for high precision analog and mixed signal applications, and have been utilized in electronic circuits of many important technological applications. The TFRs may be part of an individual device, or may be part of a complex hybrid circuit or integrated circuit. Special cares are required as integrating TFRs into existing process flows of an integrated circuit.
Generally, in fabricating a TFR in an integrated circuit, materials of the TFR are evaporated or sputtered onto a substrate wafer at a metal interconnect level and subsequently patterned and etched. As such, the TFR is embedded between the inter-metal dielectric (IMD) layers. The TFR needs an electrical connection. Therefore, two extra mask layers are required to form the TFRs itself and to form the contact points of the TFR. Conventionally, the connection of TFRs and other devices within an integrated circuit is made from an overlying metal interconnect layer to the contact points of the TFRs. The contact points of the TFRs are required to protect the resistor during via etch, which is the process to contact the overlying metal interconnect layer and the resistor.
Therefore, the cost of fabrication of an integrated circuit with TFRs is increased by additional masks for TFRs. Besides, process margin and the reliability of the integrated circuit produced are also limited by multiple deposition and dry/wet etch steps which are required to incorporate TFRs into the integrated circuit. Accordingly, improvements in structures and methods of forming the integrated circuit with TFRs continue to be sought.